1. Field of Invention
The present invention relates to a novel epoxy resin curing system which comprises of a cationic latent catalytic curing agent containing a hexafluoroantimonate, which is designed to cause an expansion of volume at the time of curing reaction. It also relates to an epoxy resin cured product obtainable by curing said epoxy resin curing system and to a method for the production of the epoxy resin cured product.
2. Background of Invention
The conventional thermosetting resins are accompanied by a shrinkage of volume of approximately 3% to 15% on curing. Such a shrinkage of volume may lead to many problems. For example: it deteriorates the dimensional stability of the cured products; it deteriorates the attachment between the substrate and the medium and thus, it leads to the occurrence of pores (formed from remaining air bubbles) or microcracks when manufacturing an elaborate adhesive and a composite matrix having good physical properties. In order to avoid the shrinkage of the cured products, fillers were utilized at the initial stage, but their use has resulted in many problems including damage to the surface of the mold.
Thereafter, spiro-ortho compounds, which do not exhibit a shrinkage of volume or show a little expansion of volume at the time of polymerization (polymerization aimed at curing), have been introduced. However, the spiro-ortho compounds also have problems in that the process for synthesizing the compounds is very complex. In addition, the applicability of the epoxy resin cured products obtained by copolymerizing the epoxy resin and a spiro-ortho compound used in the curing reaction has been restricted since their glass transition temperatures are very low, which in turn causes residual stress. These spiro-ortho compounds may exhibit approximately 25% of volume expansion when they are heated. However, when they are mixed with an epoxy resin, it is impossible to effectively suppress the shrinkage of volume owing to the curing reaction of the epoxy resin since an expansion of volume arises in addition to the curing reaction of the epoxy resin. As a result, it has been difficult to acquire the balance between physical properties in the entire curing systems and cured products obtained by the curing of the said curing systems. Accordingly, such expandable resins have inferior applicability when employed as structural materials requiring the balance between the entire mechanical properties. Generally, the term “curing systems” refers to the reaction systems which contain resins such as thermosetting resins and are introduced in a curing reaction by heat and the like.